7721

7721 is also designated D3A. Completed sales put the typical price at $86.12 per tube.

Description

The 7721 is a miniature pentode designed for rf broadband amplifiers in telecommunication systems. It is also useful in low-noise input stages, frequency multipliers, and pulse and distributed amplifiers. Features include low noise and high transconductance. When used in on-off control applications, the 7721 will maintain its emission capabilities after long periods of operation under cutoff conditions. The average life of the 7721 is more than 10,000 hours.

Construction

The 7721 has a T-6-1/2 envelope and a miniature button base, 9 pin, E9-1. It weighs approximately 10 gm and can be mounted in any position.

Ratings

The Siemens & Halske datasheet gives maximum plate voltage at zero plate current as 400 Vdc and maximum plate voltage as 220 Vdc, with maximum plate dissipation of 4.2 W. Maximum grid No. 2 voltage at zero grid No. 2 current is 400 Vdc, maximum grid No. 2 voltage is 180 Vdc, and maximum grid No. 2 dissipation is 1.0 W. Maximum negative grid No. 1 voltage is 30 Vdc; maximum positive grid No. 1 voltage is 0 Vdc. Maximum grid No. 1 resistor is 0.5 Meg, maximum cathode current is 30 mAdc, and maximum heater positive with respect to cathode voltage is 60 V, with maximum heater negative with respect to cathode voltage of 120 V. Maximum heater-cathode resistor is 20000 ohms, and maximum bulb temperature is 190 °C.

Heater

The 7721 heater voltage is 6.3 V with a heater current of 315 ± 16 mA. The heater is indirect by AC or DC, parallel supply.

Characteristics

At a plate supply voltage of 190 Vdc, grid No. 3 voltage of 0 Vdc, grid No. 2 supply voltage of 160 Vdc, grid No. 1 supply voltage of +10 Vdc, and a cathode resistor of 400 ohms, typical values include a transconductance of 35000 µmhos, a plate current of 22 mAdc, a grid No. 2 current of 6 mAdc, an amplification factor of grid No. 2 with respect to grid No. 1 of 80, a plate resistance of 0.12 Meg, and an equivalent grid noise resistance of 150 ohms. At a plate supply voltage of 160 Vdc, grid No. 3 voltage of 0 Vdc, grid No. 1 supply voltage of +10 Vdc, and a cathode resistor of 470 ohms, typical values include a transconductance of 41000 µmhos, a plate current of 24 mAdc, an amplification factor of 77, a plate resistance of 1900 ohms, and an equivalent grid noise resistance of 65 ohms.

The Siemens & Halske datasheet gives a transconductance phase angle at 100 Mc of 22 degrees, measured with the two cathode connections in parallel. Input capacitance without external shield is 10 ± 1.0 μμf; with external shield it is 10.1 ± 1.0 μμf. At a cathode current of 28 mAdc, input capacitance is 17 μμf without external shield and 17.1 μμf with external shield. Output capacitance is 2.1 ± 0.3 μμf without external shield and 3.3 ± 0.4 μμf with external shield. Input conductance at 100 Mc is 1000 µmhos, and the figure of merit is 230 Mc. Negative grid current is less than 0.3 μAdc.

Insulation

The Siemens & Halske datasheet gives grid to all interelectrode resistance at 50 Vdc as greater than 200 Meg, plate to all interelectrode resistance at 300 Vdc as greater than 500 Meg, and heater to cathode interelectrode resistance at 10 V as 20 Meg for both heater negative and heater positive with respect to cathode.

Equivalence is asserted only where the archive's own literature states it directly, in at least 40 separate documents. Tubes that merely substitute in some circuits are not listed here.

Per-tube prices from completed sales, 2026-07-09 to 2026-10-02. Matched pairs and quads are divided out. See the price index for how these move over time.

Original manufacturer datasheets for 7721, hosted by Frank Philipse's Electron Tube Data sheets.

Documents held here and used to write this page.

• $\begin{array}{c} \text{Characteristics} \\ I_{\text{b}}, I_{\text{c2}} = \textit{f}\left(\textit{E}_{\text{c1}}\right) & I_{\text{b}}, I_{\text{c2}} = \textit{f}\left(\textit{E}_{\text{b}}\right) \end{array}$
• GRENZDATEN BESONDERE ANGABEN (filed under D3A)